The overall objective of the proposed research is to study regulatory processes of the immune systems. More specifically, experiments to define a biological function(s) for IgD, the possible interaction(s) of the IgD bearing cells (or their subcellular products) with T cells and the significance of IgD on malignant B-cells are proposed. The basic approach is to use different anti-immunoglobulin reagents (anti-mu and anti-delta) to manipulate events in ontogeny and immune responses. In vivo experiments will study the effects of anti-immunoglobulin reagents on serum immunoglobulin and immunoglobulin bearing lymphocytes by administering antisera to neonatal and adult rats. In vitro experiments will study the ability of anti-delta and anti-mu reagents (1) to induce blastogenesis and the events following stimulation (differentiation of the B cells and possible enhanced stimulation of the T cells) and (2) to alter primary and secondary antibody responses in culture. Experiments are also outlined to characterize and study immunoproliferative disorders with possible B cell origin in the rat and specifically B cell malignancies expressing surface IgD.